class Solution {
public:
    int criticalConnectionHelper(unordered_map<int, vector<int>> &graph, int n, int myNode, int myRank, vector<int> &ranks, vector<vector<int>> &res)
{
    if (ranks[myNode] != -2)
    {
        return ranks[myNode];
    }

    int lowestRank = myRank;
    ranks[myNode] = myRank;
    for(auto neighbor : graph[myNode])
    {
        if (ranks[neighbor] == myRank - 1 || ranks[neighbor] == n)
        {
            continue;
        }

        int neighborRank = criticalConnectionHelper(graph, n, neighbor, myRank + 1, ranks, res);
        lowestRank = min(lowestRank, neighborRank);
        if (neighborRank > myRank)
        {
            res.push_back({min(myNode, neighbor), max(myNode, neighbor)});
        }
    }

    ranks[myNode] = n;
    return lowestRank;
}

    vector<vector<int>> criticalConnections(int n, vector<vector<int>>& connections) {
        unordered_map<int, vector<int>> graph;

    for(auto &c : connections)
    {
        graph[c[0]].push_back(c[1]);
        graph[c[1]].push_back(c[0]);
    }

    vector<int> ranks(n, -2);
    vector<vector<int>> res;
    criticalConnectionHelper(graph, n, 0, 0, ranks, res);
    return res;
    }
};